1. Field of the Invention
The present invention relates to banding in inkjet printing, and, more particularly, to an imaging apparatus and method of using colorant density for reducing printing defects in inkjet printing.
2. Description of the Related Art
An inkjet print engine of an inkjet printer or multifunction imaging device forms an image on a print media sheet by horizontally scanning one or more inkjet printheads across the print media sheet in multiple printing passes, also referred to as printing swaths, and by indexing the print media sheet in an orthogonal direction, e.g., a vertical direction, between printing passes. Such inkjet print engines are capable of printing in multiple printing modes, e.g., draft, high quality, photo, etc.
In accordance with the present invention, it has been observed that the printing defects of dry-time banding and swath contraction are a function of colorant density on the printed page. Dry-time banding is a defect that is produced in multi-pass printing where the ink from the previous print swath applied during a previous printing pass is in a transient drying state and is contacted by ink of a next print swath applied during a next printing pass. For example, if the previous print swath was applied in a left-to-right printing pass, the beginning (left) portion of the print swat is more dry than the end (right) portion of the print swath. On the next printing pass, typically in an opposite direction, right-to-left, the beginning portion of this next print swat is applied on the wettest portion of the previous print swath, and the end portion of this next print swath is applied to the driest portion of the previous print swath. This act of printing new ink on wet ink in multiple printing passes tends to cause dry-time banding when the printing densities of the respective print swaths are high enough and in the right combination of colorants.
Swath contraction occurs when the population of the jetting nozzles in an individual inkjet array is high enough to produce an airflow wherein ink droplets near the vertically opposed ends of the inkjet array are pulled inwardly in parallel to the inkjet array. This produces an effectively shorter print swath height, i.e., in the vertical direction, which leaves white or lighter space showing at the print swath boundaries.
What is needed in the art is an imaging apparatus and method that reduces printing defects associated with dry-time banding, and swath contraction.